Polycarbonate is typically prepared in a heterogeneous reaction mixture which has an aqueous phase and an organic phase. Monitoring pH in the aqueous phase during the polycarbonate-forming reaction is often desirable for the purpose of obtaining a polycarbonate product possessing advantageous characteristics and properties. The pH of the aqueous phase may be adjusted by addition of base to the reaction mixture at one or more times during the progress of the reaction. The pH of the aqueous phase may, for example, be held substantially constant at a selected value by continual additions to the reaction mixture of small, incremental amounts of base. Or, when the addition of base occurs in larger quantities on a limited number of occasions during the process, the natural result of the polycarbonate-forming reaction may be allowed to reduce the pH as the reaction progresses.
When polycarbonate is prepared from a halogenated dihydroxy compound, and the addition of base to the reaction mixture occurs in larger quantities on a limited number of occasions, it is often difficult to accurately control the pH of the reaction mixture as the reaction progresses. It has been found, as an alternative, that the pH of the aqueous phase at the conclusion of the reaction is a useful indicator of whether the polycarbonate product will possess desirable characteristics and properties.
It is therefore a feature of this invention to provide a process for preparing halogenated polycarbonate which allows for control of the pH of the aqueous phase of the reaction mixture at the conclusion of the reaction to a selected level. An advantage of such a process is that halogenated polycarbonate having a desirably high molecular weight may be prepared thereby. It is also a feature of the process of this invention to utilize a coupling catalyst in the reaction mixture in a controlled amount, also for the purpose of obtaining a desirably high molecular weight halogenated polycarbonate.